The role of the pineal body, which is considered to be a control center of the circadian rhythm, the rod outer segmen (ROS) renewal system was studied with pinealectomized and superior cervical ganglionectomized rats. The renewal system of ROS was also examined from the developmental aspect in control and dystrophic rats. In vitro regeneration of microvilli of the pigment epithelium (PE) was observed by using the organ culture technique in these animals.